1. Field of the Invention
The present invention relates generally to an electromagnetic-induction system, and more particularly to the electromagnetic-induction system with an application specific integrated circuit (ASIC).
2. Description of the Prior Art
Because a handwriting recognition system could replace the mouse, and is more suitable than the mouse to let the user input words and patterns by user's hands, improvement of the handwriting recognition system is a hot and important field of current computer technology. The original intention of the handwriting recognition system is to replace the mouse. As usual, to enhance the user's convenience, a handwriting recognition system would usually replace the mouse by both tablet and electromagnetic-induction pen thereof. Herein, the nib of electromagnetic-induction pen usually corresponds to the left button of the mouse. Conventional handwriting recognition systems have been developed for many years, but these products are applied to perform only one function, such as drawing or inputting a word.
In the conventional system with cordless pressure-sensitivity and electromagnetic-induction, there are usually a digitizer tablet and a transducer/cursor in the form of a pen or a puck. As is well known, there are two operation modes for determining the position of a pointing device on the surface of a digitizer tablet, wherein one is a relative mode, and the other is an absolute mode. A mouse device operates in a relative mode. The computer sensing the inputs from a mouse recognizes only relative movements of the mouse in X and Y directions as it is slid over the surface on which it is resting. If the mouse is lifted and repositioned on the surface, no change in the signal to the computer will be detected. A common approach uses a sensing apparatus inside the mouse to develop a pair of changing signals corresponding to the longitudinal and transversal movements of the mouse. On the contrary, a cursor device in a digitizer tablet system, such as electromagnetic-induction pen, operates in an absolute mode. If a cursor device is lifted and moved to a new position on its supporting surface, its signal to a computer will change to reflect the new absolute position of the cursor device. Nowadays, various methods have been used to determine the position of a cursor device on the surface of its supporting tablet, wherein one common skill which is applied for the absolute mode is electromagnetic field sensing.
Early transducer/cursors were connected to the tablet by means of a multi-conductor cable through which the position and button/pressure information are transferred virtually without any problem. The cordless transducer/cursors in some of the prior arts have attempted to use frequency and/or phase changes to transmit the non-positional status of the transducer/cursor functions such as buttons pushed, pen pressure, or the like. However, if there is no sophisticated processing, frequency and phase changes are very prone to false reading resulting from several outside factors such as metal objects, noise, wireless electromagnetic wave and so on. These problems become more apparent, especially in a larger digitizer tablet. Improvements have also been made in the prior arts to allow a user to use pointing devices on a digitizer tablet system in dual modes of operation that can provide information of either a relative movement or an absolute position under the control of the user.
Usually, a handwriting recognition system is a device with cordless pressure-sensitivity and electromagnetic-induction. Refer to FIG. 1, it shows a circuit block diagram of a conventional cordless pressure-sensitive and electromagnetic-induction device. Conventional cordless pressure-sensitivity and electromagnetic-induction device comprises: an electromagnetic-induction pen and a tablet. There is an oscillating circuit that consists of LC in the electromagnetic-induction pen. If the pen point is touched, the amount of inductance will be changed that results in the variation of oscillating frequency. The amount of inductance is increased when touching the pen point and increasing pressure so the variation of oscillating frequency is also increased. Therefore, the variation of the pressure on the pen point can be detected by way of the variation of oscillating frequency. There are two switches on the sidewall of the electromagnetic-induction pen, the emitted frequency of the electromagnetic-induction pen can be changed with the capacitance variation of the LC device that is produced by pushing down or setting free the switches. Furthermore, the tablet comprises a detector, an amplifier and an analog-digital converter. In the conventional tablet, there is a detected loop in the center region of the tablet, with one-way antennas located on the double faces of the detected loop, wherein the one-way antennas are equidistantly arranged in order by way of using array. The main purpose of the one-way detected loop is only applied to receive the electromagnetic wave that is emitted by the electromagnetic-induction pen. When the electromagnetic-induction pen emits the electromagnetic wave, the one-way antennas receive the electromagnetic wave, and then the tablet can obtain correlative information by the electromagnetic induction.
In general, because the design of conventional electromagnetic-induction apparatus is restricted by amount of devices and cost thereof, it only use the programmable amplifier with eight-level gain at the utmost, that is, the programmable amplifier has eight gain-scope of band thereof at the utmost, so that the gain-control is performed by using the analogy switches are eight at the utmost. The various gain-value can be chosen according to degree of signal (strong or weak). When the signal with the large variation transmitted into the analogy switches, the saturated signal is due to eight-level gain at the utmost that results in the handwriting defect, especially, it is harmful to linear. Furthermore, a plurality of adders and subtracters are commonly designed and employed in the conventional electromagnetic-induction apparatus so as to calculate the data. Particularly, when the conventional electromagnetic-induction apparatus applies the central processing unit (CPU) with low speed, it must use the plurality of adders and subtracters to simulate the operations of multiplication and division that results in reduction of the report rate of the electromagnetic-induction apparatus. Moreover, the conventional electromagnetic-induction apparatus outputs the frequency signal by using a program and then the analogy switch transmits it to antenna, so that the frequency signal with unsteady state is generated. Therefore, the central processing unit (CPU) continuously proceeds to the operation that results in increase of processing time thereof. Also, the electromagnetic pen receives the unstable power whereby the digital tablet inducts the energy with unsteady state. On the other hand, in order to reduce the cost in the conventional electromagnetic-induction apparatus, the data are directly obtained from the frequency counter that causes the accessed data from the frequency counter are unstable too.
In accordance with the above description, a large amount of electronic devices are employed for designing the conventional electromagnetic-induction apparatus to additionally combine with the printed circuit board (PCB) and the cost are increased. Additionally, some of the devices with various functions are difficult to be installed into the finite space within the electromagnetic-induction apparatus that limits development of functions within the electromagnetic-induction apparatus. Moreover, it is necessary that many analogy devices are also employed for designing the conventional electromagnetic-induction apparatus, so that the quality is reduced, also. In view of these, an application specific integrated circuit (ASIC) of the electromagnetic-induction system is therefore necessary, so as to strengthen and increase the functions of the electromagnetic-induction apparatus.